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At least 811 records · Page 45Linked to original sources
PubMed2006

Report: anaerobic digestion of a sulphate-rich high-strength landfill leachate: the effect of differential dosing with FeCl3.

The effect of different dose concentrations of FeCl3 on the performance of a mesophilic anaerobic digester treating a highly alkaline, high-strength and sulphate-rich landfill leachate was tested. The results indicated that sulphate reduction was the predominant reaction and methanogenic processes were entirely inhibited in the reactor without FeCl3 addition. Adding FeCl3 into the reactor restored some methanogenic activity and also improved the rates of sulphate reduction. A combination of sulphate reduction and methanogenic activity resulted in up to 75% chemical oxygen demand (COD) removal and 85% sulphate removal. Sulphate reduction remained the principle mechanism by which COD removal took place with a methane yield of only between 0.14 and 0.18 m3 CH4 kg(-1) COD removed being achieved. The process was, however, stable and offered advantages for the further treatment or conveyance of the anaerobically treated leachate.

Anaerobiosis↗
PubMed1985

Copper(II)- and iron(II)-complexes of methyl 2-(2-aminoethyl)-aminomethyl-pyridine-6-carboxyl-histidinate (AMPHIS), a peptide mimicking the metal-chelating moiety of bleomycin. An ESR investigation.

Methyl 2-(2-aminoethyl)-aminomethyl-pyridine-6-carboxyl-histidinate (AMPHIS), a synthetic analogue of the chelating part of bleomycin (BLM), has been studied for its metal binding properties. Electron spin resonance parameters of AMPHIS-Cu(II) and BLM-Cu(II) have been found to be closely similar likewise spectra of oxygen radicals spin-adducts induced by AMPHIS-Fe(II)-O2 and BLM-Fe(II)-O2 systems. Thus, AMPHIS could constitute a very useful tool for the study of BLM mode of action.

Binding Sites↗
PubMed2000

Critical oxygen tension in rat brain: a combined (31)P-NMR and EPR oximetry study.

The relationship between cerebral interstitial oxygen tension (Pt(O(2))) and cellular energetics was investigated in mechanically ventilated, anesthetized rats during progressive acute hypoxia to determine whether there is a "critical" brain Pt(O(2)) for maintaining steady-state aerobic metabolism. Cerebral Pt(O(2)), measured by electron paramagnetic resonance oximetry, decreased proportionately to inspired oxygen fraction. (31)P-nuclear magnetic resonance measurements revealed no changes in P(i), phosphocreatine (PCr)/P(i) ratio, or intracellular pH when arterial blood oxygen tension (Pa(O(2))) was reduced from 145.1 +/- 11.7 to 56.5 +/- 4.4 mmHg (means +/- SE). Intracellular acidosis, a sharp rise in P(i), and a decline in the PCr/P(i) ratio developed when Pa(O(2)) was reduced further to 40.7 +/- 2.3 mmHg. The corresponding Pt(O(2)) values were 15.1 +/- 1.8, 8.8 +/- 0.4, and 6.8 +/- 0.3 mmHg. We conclude that over a range of decreasing oxygen tensions, cerebral oxidative metabolism is not sensitive to oxygen concentration. Oxygen becomes a regulatory substrate, however, when Pt(O(2)) is decreased to a critical level.

Animals↗
PubMed1980

Decomposition of the neuro- and nephrotoxic compound dichloroacetylene in the presence of oxygen: separation and identification of novel products.

Dichloroacetylene (DCA) shows pronounced nephrotoxic effects in several animal species and is neurotoxic in humans. It is a chemically highly reactive compound that decomposes spontaneously in the presence of oxygen. The chemical decomposition of DCA has been studied in order to understand the role of the decomposition products for the toxic effects of DCA. Seven compounds were identified by their mass spectra and by comparison with authentic reference materials. Among these were phosgene, hexachlorobutadiene, and other reactive products (e.g., trichloroacetyl chloride and trichloroacryloyl chloride), which may explain, in part, the toxicity of DCA.

Acetylene↗
PubMed1988

Effect of various oxygenation conditions and fluosol-DA on cancer chemotherapeutic agents.

Adding Fluosol-DA and carbogen breathing to treatment with various anticancer drugs can result in a significant enhancement of tumor growth delay compared to the drug and air breathing. The optimal conditions for tumor response depend upon the drug, oxygenation level and duration, and perfluorochemical emulsion dosage. In this study, representative chemotherapeutic agents from several classes were tested in a tumor growth delay assay in combination with various doses of Fluosol-DA under conditions of normal aeration, carbogen breathing either for 1-2 hours or 6 hours, or with hyperbaric 100% oxygen (3 atmospheres) breathing for 1 hour to determine whether the antitumor activity of these drugs would be improved.

Animals↗
PubMed2005

Non-invasive measurement of tumor oxygenation using embedded microparticulate EPR spin probe.

We have developed a novel procedure for in situ monitoring of oxygen concentration in growing tumors by electron paramagnetic resonance (EPR)-based oximetry using embedded paramagnetic particulates. The new approach uses spin probes that are permanently embedded or implanted in the tumor. A particular advantage of this procedure is that it is non-invasive, both in terms of implantation of the probe as well as readouts of oxygen. We implanted a mixture of RIF-1 tumor cells and microparticulates of lithium phthalocyanine (LiPc) in the upper hind leg of C3H mice to grow as solid tumor. This enabled repeated measurements of oxygen concentration from the implanted site (tumor) for more than two weeks during the progression of the tumor. The particulates that were embedded in the tumor were stable and non-toxic to tumor cells. There was no apparent inhibitory effect to cell proliferation or tumor growth rate. The measurements indicated that the PO2 of the tumor decreased exponentially with tumor growth (size) and reached hypoxia (< 4 mm Hg). EPR imaging was used to identify the distribution of the particles in the tumor. The data showed a heterogeneous distribution of the probe particles within the tumor volume. Imaging of oxygen in the growing tumor demonstrated the development of significant hypoxia in the tumor within 4-6 days after inoculation. In summary, the EPR spectroscopy and imaging using embedded spin probe enabled accurate and repeated measurements of PO2 under non-perturbing conditions in growing tumors.

Animals↗
PubMed1972

Effect of four nematocides on activities of microorganisms in soil.

Tests were conducted to determine the effects of four nematocides, Dasanit, carbofuran, D-D, and Vorlex on microbial activities in a loamy sand. The results indicated that bacterial and fungal populations initially decreased with some nematocide treatments but recovered rapidly to levels similar to those in the controls. In some instances, ammonium production from added peptone increased in the nematocide-treated soils, whereas mineralization of soil organic nitrogen and nitrification and oxidation of elemental sulfur were depressed. Oxygen consumption generally increased in proportion to the concentration of nematocide in the soil. However, with Vorlex, an increase in respiration was evident at the lower concentration, whereas an inhibitory effect occurred at the higher concentration. The study indicated that indigenous soil microorganisms can tolerate these chemicals used for control of nematodes in soil.

Ammonia↗
PubMed1987

Effect of inhibition of glutathione reductase by carmustine on central nervous system oxygen toxicity.

Exposure of animals to O2 at increased partial pressures above 2.5 atmospheres absolute results in seizures. The endogenous intracellular antioxidant defense mechanisms are thought to play a protective role in mitigating such seizures. Investigations were carried out to determine if inhibiting brain glutathione reductase with carmustine would result in an alteration in time to seizures of rats exposed to high pressure O2. Treatment of air-breathing rats with carmustine (12.5, 25 and 50 mg/kg i.v.) resulted in a dose-dependent decrease (P less than .001) in whole-brain glutathione reductase activity without affecting the activities of the other components of the antioxidant defense mechanisms determined. This treatment also resulted in a dose-dependent decrease (P less than .001) in time to seizure of rats exposed to four atmospheres absolute O2. Conversely, treatment of rats with lomustine (30 mg/kg i.v.), a nitrosourea compound related to carmustine, failed to affect the activity of brain glutathione reductase or any other component of the antioxidant defense mechanism determined, or did it influence the seizure time of rats exposed to four atmospheres absolute O2. These results suggest that glutathione reductase is an integral component of the antioxidant defense mechanisms. Inhibition of this enzyme results in an alteration in sensitivity of the organism to the toxic effects of O2.

Animals↗
PubMed2002

Low molecular weight hyaluronic acid prevents oxygen free radical damage to granulation tissue during wound healing.

Hyaluronic acid protects granulation tissue from oxygen free radical damage and stimulates wound healing, but its molecular weight prevents it from permeating the epidermal barrier A low molecular weight hyaluronic acid preparation is able to permeate the skin, but it is unknown whether or not it retains the scavenging effects of oxygen free radicals in granulation tissue. Our experiments were conducted in rats with excisional or incisional wounds. Wound contraction over 11 days and breaking strength on the fifth day were measured. Oxygen free radical production was induced by intraperitoneal administration of two different xenobiotics: phenazine methosulfate and zymosan. The wounds were treated topically with low molecular weight hyaluronic acid (0.2%) cream or placebo. In the incisional wound group, the effects of superoxide dismutase were also determined. Absolute controls received wounds and placebo but no xenobiotics. Wound healing was significantly slower in the xenobiotic group than in the control groups. These effects were strongly reduced by topical administration of low molecular weight hyaluronic acid (0.2%) cream and in incisional wounds by topically injected superoxide dismutase. Low molecular weight hyaluronic acid is effective as the native compound against oxygen free radicals. Its pharmacological effects through transdermal administration should be tested in appropriate models.

Granulation Tissue↗
PubMed1979

The reaction of cytochrome oxidase with oxygen in the fission yeast Schizosaccharomyces pombe 972h-. Studies at subzero temperatures and measurement of apparent oxygen affinity.

1. Cytochrome alpha 3 in whole-cell suspensions of the fission yeast Schizosaccharomyces pombe reacted in the reduced form with CO to give a photodissociable CO complex with absorption maxima at 429, 543 and 591 nm in CO-liganded reduced-minus-reduced difference spectra. 2. Other CO-bound haemoproteins, cytochromes P-420 and P-450, were not photodissociated under the conditions employed. 3. Measurements of the rates of reassociation of CO with cytochrome alpha 3 after flash photolysis over the temperature range from -101 to -109 degrees C gave a value for Eact. of 28.6 kJ/mol. 4. Between -94 and -106 degrees C, O2 reacted with cytochrome oxidase in intact cells to give an oxygenated intermediate (compound A). 5. At -70 degrees C compound A was converted into a second spectrally distinct intermediate (compound B). 6. Electron transport, indicated by the oxidation of cytochromes alpha + alpha 3 and cytochrome c, did not occur until the temperature was raised to -50 degrees C. 7. At room temperature cytochfome oxidase was oxidized to 50% of its steady-state concentration by 0.35 microM-O2.

Ascomycota↗
PubMed1997

Myocardial oxygen tension and capillary density in the isolated perfused rat heart during pharmacological intervention.

Oxygen is essential for normal cardiac function and plays an important role in cardiac regulation. Electron paramagnetic resonance (EPR) oximetry appears to have some significant advantages for measuring oxygen tension (pO2) in the beating heart. This study presents the serial measurement of myocardial pO2 by EPR oximetry in the isolated crystalloid perfused heart during treatment with different cardioactive drugs: dobutamine, metoprolol, verapamil, vasopressin, and N omega-Nitro-L-Arginine Methyl Ester (L-NAME). Baseline myocardial pO2 was 176 +/- 14 mmHg (mean +/- S.E.). Myocardial capillary density in the intact contracting heart was calculated to be 2300 +/- 100 mm-2, using local myocardial pO2 and a cylindrical model for oxygen diffusion in tissue. Each drug had characteristic effects on myocardial pO2, myocardial oxygen consumption (MVO2), and capillary density. Metoprolol and verapamil increased myocardial pO2 by 51% and 18%, respectively, dobutamine decreased myocardial pO2 by 84% while vasopressin and L-NAME had no significant effect on myocardial pO2. Metoprolol and verpamil decreased MVO2 by 9% and 56%, respectively, while dobutamine increased MVO2 by 59%. A quantitative comparison of effects on the capillary bed based on changes in myocardial pO2 and MVO2 was made. Metoprolol and verapamil had opposite effects on the capillary bed. Verapamil decreased myocardial capillary density by 39%, while capillary density increased by 10% (n.s.) with metoprolol. Data following perfusion without drug is also presented. We conclude that: 1) The application of EPR oximetry with LiPc provides dynamic evaluation of local myocardial pO2 in the contracting heart. 2) Using a cylindrical model of oxygen delivery and diffusion in tissue, these data may be used to describe the changes of capillary density during pharmacological interventions.

Adrenergic beta-Agonists↗
PubMed2004

S-nitroso human serum albumin improves oxygen metabolism during reperfusion after severe myocardial ischemia.

Nitric oxide (NO) supplementation may modify myocardial oxygen consumption and vascular function after ischemia. We investigated the effects of the NO donor, S-nitroso human serum albumin (S-NO-HSA), on cardiac oxygen metabolism during controlled reperfusion on normothermic cardiopulmonary bypass after severe myocardial ischemia. Pigs randomly received either S-NO-HSA or human serum albumin prior to and throughout global myocardial ischemia. Myocardial oxygen utilization is impaired at the onset of reperfusion, which is not amenable to S-NO-HSA. However, NO supplementation during ongoing supply dependency of oxygen consumption eventually leads to greater myocardial oxygen delivery and consumption. In conjunction with a better washout of lactate, this indicates an improved capillary perfusion in the S-NO-HSA group during reperfusion, which results in a better contractile function post bypass.

Animals↗
PubMed2000

Oxidative mutagenesis in Escherichia coli strains lacking ROS-scavenging enzymes and/or 8-oxoguanine defenses.

Escherichia coli strains with different combinations of null mutations in the katG, katE, sodA, sodB, fpg, and mutY genes were constructed to compare their spontaneous mutation frequencies and sensitivities to various oxidants with those of bacteria solely deficient in catalase (katG katE) or cytosolic superoxide dismutase (sodA sodB) and the parental strain possessing a full complement of these enzymes. The MutY DNA glycosylase represented the major protection against the mutagenic consequences of processes associated with normal aerobic metabolism. Spontaneous mutagenesis in MutY-lacking bacteria was not influenced by the absence of (A)BC excinuclease or the presence of MucAB proteins, a result consistent with 8-oxoguanine being a principal premutational lesion. In contrast, catalase and SOD represented the major protection against the genotoxic consequences of bursts of oxidative stress caused by reactive-oxygen-generating compounds. Therefore, only bacteria simultaneously defective in both katG and katE or sodA and sodB genes were hypersensitive with respect to mutability by peroxide and superoxide, respectively. These data suggest that oxidative lesions other than 8-oxoguanine contribute to mutagenesis by hydrogen peroxide and redox-cycling chemicals.

DNA Repair↗
PubMed2006

General route to racemic and enantiomeric carbo- and heterocyclic vinyl sulfoxides via tandem Michael addition/Horner olefination of alpha-phosphorylvinyl sulfoxides.

A new one-pot synthesis of heterocyclic and carbocyclic vinyl sulfoxides has been developed which involves reaction of alpha-phosphorylvinyl sulfoxides with carbonyl compounds bearing oxygen, nitrogen, and carbon nucleophilic centers. Use of optically active alpha-phosphorylvinyl p-tolyl sulfoxides in this tandem Michael addition/Horner olefination reaction leads to the corresponding optically active cyclic sulfoxides. In this way, a variety of optically active chromene, pyrrolizine, chinoline, and cyclopentene sulfoxides have been efficiently prepared.

Alkenes↗
PubMed2005

Titanium, zinc and alkaline-earth metal complexes supported by bulky O,N,N,O-multidentate ligands: syntheses, characterisation and activity in cyclic ester polymerisation.

The reactions of the bulky amino-bis(phenol) ligand Me(2)NCH(2)CH(2)N[CH(2)-3,5-Bu(t)(2)-C(6)H(2)OH-2](2)(1-H(2)) with Zn[N(SiMe(3))(2)](2)(4), [Mg[N(SiMe(3))(2)](2)](2)(5) and Ca[N(SiMe(3))(2)](2)(THF)(2)(6) yield the complexes 1-Zn, 1-Mg and 1-Ca in good yields. The X-ray structure of 1-Ca showed the complex to be dimeric, with calcium in a distorted octahedral coordination geometry. Five of the positions are occupied by an N(2)O(3) donor set, while the sixth is taken up by an intramolecular close contact to an o-Bu(t) substituent, a rare case of a Ca...H-C agostic interaction (Ca...H distances of 2.37 and 2.41 Angstroms). Another sterically hindered calcium complex, Ca[2-Bu(t)-6-(C(6)F(5)N=CH)C(6)H(3)O](2)(THF)(2).(C(7)H(8))(2/3)(7), was prepared by reaction of 6 with the iminophenol 2-Bu(t)-6-(C(6)F(5)N=CH)C(6)H(3)OH (3-H). According to the crystal structure 7 is monomeric and octahedral, with trans THF ligands. The complex Ti[N[CH(2)-3-Bu(t)-5-Me-C(6)H(2)O-2](2)[CH(2)CH(2)NMe(2)]](OPr(i))(2)(2-Ti) was prepared by treatment of Ti(OPr(i)(4)) with the new amino-bis(phenol) Me(2)NCH(2)CH(2)N[CH(2)-3-Bu(t)-5-Me-C(6)H(2)OH-2](2)(2-H(2)). The reduction of 2-Ti with sodium amalgam gave the titanium(III) salt Ti[N[CH(2)-3-Bu(t)-5-Me-C(6)H(2)O-2](2)[CH(2)CH(2)NMe(2)]](OPr(i))(2).Na(THF)(2)(8). A comparison of the X-ray structures of 2-Ti and 8 showed that the additional electron in 8 significantly reduced the intensity of the pi-bonding from the oxygen atoms of the isopropoxide groups to titanium. 1-Ca and 8 were active initiators for the ring-opening polymerisation of epsilon-caprolactone (up to 97% conversion of 200 equivalents in 2 hours) and yielded polymers with narrow molecular weight distributions.

Biocompatible Materials↗
PubMed2002

A basic study of some normoxic polymer gel dosimeters.

Polymer gel dosimeters offer a wide range of potential applications in the three-dimensional verification of complex dose distribution such as in intensity-modulated radiotherapy (IMRT). Until now, however, polymer gel dosimeters have not been widely used in the clinic. One of the reasons is that they are difficult to manufacture. As the polymerization in polymer gels is inhibited by oxygen, all free oxygen has to be removed from the gels. For several years this was achieved by bubbling nitrogen through the gel solutions and by filling the phantoms in a glove box that is perfused with nitrogen. Recently another gel formulation was proposed in which oxygen is bound in a metallo-organic complex thus removing the problem of oxygen inhibition. The proposed gel consists of methacrylic acid, gelatin, ascorbic acid, hydroquinone and copper(II)sulphate and is given the acronym MAGIC gel dosimeter. These gels are fabricated under normal atmospheric conditions and are therefore called 'normoxic' gel dosimeters. In this study, a chemical analysis on the MAGIC gel was performed. The composition of the gel was varied and its radiation response was evaluated. The role of different chemicals and the reaction kinetics are discussed. It was found that ascorbic acid alone was able to bind the oxygen and can thus be used as an anti-oxidant in a polymer gel dosimeter. It was also found that the anti-oxidants N-acetyl-cysteine and tetrakis(hydroxymethyl)phosphonium were effective in scavenging the oxygen. However, the rate of oxygen scavenging is dependent on the anti-oxidant and its concentration with tetrakis(hydroxymethyl)phosphonium being the most reactive anti-oxidants. Potentiometric oxygen measurements in solution provide an easy way to get a first impression on the rate of oxygen scavenging. It is shown that cupper(II)sulphate operates as a catalyst in the oxidation of ascorbic acid. We, therefore, propose some new normoxic gel formulations that have a less complicated chemical formulation than the MAGIC gel.

Acetylcysteine↗
PubMed1975

Iron-deficiency anemia: evaluation of compensatory changes.

Compensatory mechanisms in children with iron-deficiency anemia were evaluated by measuring erythrocytic organic phosphates and, in some cases, shifts in the P50 of the oxygen dissociation curve. In 19 children with nutritional anemia (hemoglobin values of 3.2 to 8.2 gm/dl) there was a calculated improved oxygen delivery to tissues equivalent to a hemoglobin level of at least 7.5 gm/dl. Transient decompensation was observed during acidosis. In five children with iron-deficiency anemia due to blood loss and in one child with rheumatoid arthritis no such compensatory changes were observed.

Adenosine Triphosphate↗